Method for manufacturing concrete pressure vessels



A. ZIEGLER June 25, 1968 METHOD FOR MANUFACTURING CONCRETE PRESSUREVESSELS 2 Sheets-Sheet l Filed June 26, 1963 June 25, 1968 A. ZIEGLER3,390,211

METHOD FOR MANUFACTURING CONCRETE PRESSURE VESSELS Filed June 26, 1963 2Sheets-Sheet 2 United States Patent O 3.390 211 METHOD FR MANUFCTURINGCONCRETE PRESSURE VESSELS Albert Ziegler, Erlangen, Germany, assignor toSiemens Aktiengesellschaft, Munich, Germany, a corporation of GermanyFiled June 26, 1963, Ser. No. 290,733 Claims priority, applicationGermany, Mar. 2, 1963,

4 claims. (ci. zat- 32) My invention relates to a method ofmanufacturing concrete pressure vessels, and more particularly toprestressed concrete pressure vessels for nuclear reactors.

Pressure vessels of exceptionally large diameter are often necessary fornuclear power reactors. Pressure vessels consisting of steel, whichcannot be of high grade type generally because of the effect of fastneutrons, can be transported great distances only if their diameter doesnot exceed about live meters. The manufacture and transportation oflarger vessels present considerable difficulties, and these vessels mustbe at least partly welded together at the construction site, in whichcase additional difficulties and cost are encountered by the necessityof eliminating tension of annealing the welded structures.

Construction of concrete radiation shielding simultaneously with thepressure vessels for gas-cooled nuclear reactors has been attempted,These pressure vessels are erected with concrete that is prepared at theconstruction site. For pressurized water reactors difficulties arise inthis method of construction, due to the high pressure of over 100kp./cm.2 (metric kilopounds per sq. cm.), because the bracing orreinforcing wires in the concrete must be very thick and the compressivestress of the concrete can amount to as much as 300 kp./cm.2.

lt is an object of my invention to provide a method of manufacturing apressure vessel of prestressed concrete suitable for pressurized waterreactors and a method of constructing the same at the erection site ofthe reactor thereby avoiding the aforementioned difficulties.

To this end, and according to a feature of my invention, the innercavity of the vessel is assembled of prefabricated parts and is equippedwith prestressing elements; and the vessel, after being assembled, isput under the rated pressure, whereafter the thereby widened butt gapswhich develop between the components or parts thereof are filled withpressure-resistant material. For applying internal pressure to thevessel up to the rated pressure value, a balloon of leakproof andeleastic material, for example rubber, is inserted into the interior ofthe vessel and is inflated with a fluid, preferably with water. Thewidened butt gaps are covered on the inside of the vessel with strips ofpressure-resistant material, for example of steel, while the pressure isbeing built up. The component parts of the vessel include, for example,segments of the vessel wall that are trapezoidal in cross section and atleast one insert adapted to tit into an opening in the wall.

According to a further aspect of my invention, the trapezoidal segmentsmay be prestressed by a type of prestressing means referred tohereinafter as prestressing means of a lirst kind such as longitudinallyextending bracing wires or the like. With trapezoidal components of thistype, vessels of spherical, cylindrical or ellipsoidal shape and ofvarious other shapes can be assembled. Such a vessel can however also beassembled of prestressed or non-prestressed, annular or semiannular wallsegments or of wall segments shaped like regular polygons, such asequilateral triangles, regular hexagons, and the like. In those cases inwhich the wall segments proper are not prestressed, the prestressingmeans for the assembled vessel can be, for example,

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steel bands disposed in a reticular or grid-like arrangement, or a steelshell tightly covering the outer wall surface. After the assembly ofcylindrical or ellipsoidal vessels in which prestressed wall segments ofthis type are used, there are mounted thereon additional prestressingelements referred to hereinafter as prestressing means of a second kindwhich have, for example the form of annular cables or cable loops.

According to another aspect of my invention, in order to reduce theintensity of radiation coming from the reactor to such an extent thatthe heat evolving in the concrete does not exceed a predeterminedquantity, the inner surfaces of the casing segments are clad with atleast one layer of a substance of great density and high thermalconductivity. The layer can, for example consist of a thick steel plateor of several thin plates superimposed one on the other, The steelplates which can have a thickness up to about 2O centimeters can beprewelded and can be used as so-called dead sheathing. At the abuttingedges of the steel plates there are advantageously provided guidingstrips which overlap one another 4after the pressure vessel has beenassembled. The side of the plates facing the concrete is preferablycooled by water or gas. For this purpose, cooling pipes can for examplebe welded to the back of the steel plates and may be embedded in thepoured concrete. When several superimposed steel plates are provided,the coolant can also be conducted through channels that are disposedbetween the individual steel plates. The inner and outer surfaces of thewall segments are, for example, curved in such a manner that both theinner chamber and the outer contour of the vessel are ellipsoidal inform.

According to a furthe-r aspect of my invention, the lower insert is madeof concrete, for example, and the upper insert of steel. An accessopening is provided, for example in the upper insert, while passagewaysare provided in the lower insert and, possibly also in the upper insertor in the vessel wall, for the necessary coolant inlet and dischargepipes, for electrical lines and the like. A thin layer of austeniticsteel is coated on the inner side of the steel plates inside the chamberof the pressure vessel. This sealing layer extends outwardly between theinner surfaces of the wall segments and the upper insert, and is securedto the layer of steel plates above the upper insert by means of asuitable end welding process. The pressure vessel can consequently thenbe opened by simply lowering the upper insert into the vessel.

A number of embodiments of my inventive pressure vessel is shown in thedrawings which will further explain Qthe invention as follows. They showFIG. l is a longitudinal sectional view' of one embodiment of aprestressed concrete pressure vessel constructed in accordance with myinvention;

FIG. 2 is a transverse sectional view of FIG. 1 along the line II-IItaken in the direction of the arrows;

FIG. 3 is a longitudinal section of a second embodiment of theinvention;

FIG. 4 is a transverse sectional view of FIG. 3 along the line IV-IVtaken in the direction of the arrows;

FIG. 5 is a longitudinal sectional View of yet another embodiment of theinvention;

FIG. 6 is a side view of a wall segment of the invention, showing indot-dash and in broken lines, the outline of the wall segment underditferent conditions of prestressing;

FIG. 7 is a fragmentary sectional view of the inner lining of a pressurevessel constructed in accordance with the invention before stressing;

FIG. 8 shows the lining of FIG. 7 after stressing;

FIG. 9 shows the lining of FIG. 7 in nal condition;

FIG. l() is a fragmentary section through the vessel Wall showing amodified inner lining which is provided with cooling pipes;

FIG. 11 is a transverse view of FIG. 10 along the line XI-XI taken inthe direction of the arrows;

FIGS. 12 and 13 are fragmentary sections of two additional modificationsof the inner lining, in which the inner lining is formed of a pluralityof layers and is also provided with cooling channels.

Referring rst to FIGS. 1 and 2, there is shown a pressure vessel for anuclear reactor assembled for example of sixteen Wall segments 11 havinga trapezoidal cross section, a lower end block 12 and an upper end block13. The prefabricated wall segments 11 are shaped in such manner thatboth the inner chamber and the outer shape of the vessel are ellipsoidalin form. The segments 11 are prestressed in the longitudinal directionwith bracing wires 15 that are embedded in the concrete, and areprovided at their ends with suitable locking means 16. The outer edgesof the casing segments 11 are bevelled or charnfered. Extending from thechamfered outer edges 17 are annular cables 18 which are introduced intopipes 19 that are embedded in concrete and provided for this purpose,and after having `been wound around once or several times, are secured,respectively, by their ends to the chamfered outer edges 17 by suitablelocking means such as the turnbuckle 20.

The surfaces of the casing segments that face the core or nuclearfission zone 14 of the reactor are clad with thick steel plates 21 whichprovide a complementary inner lining for the pressure vessel and therebyprotect the concrete against the effects of radiation and heat. Theinner lining of the vessel can also consist of Several platessuperimposed one on the other. Instead of steel, -another material withgreat density and high thermal conductivity can be employed. For coolingthe inner lining 21, cooling pipes 40 (FIGS. 10 and 1l) supplied with aliquid or gaseous coolant are provided, for example on the side thatfaces the concrete, or, where the lining consists of several layersprovision is made for cooling channels 43, 49 in FIGS. l2 and 13respectively that are arranged between these layers. The abutting edgesof the steel plates 21 which are Welded to the casing segments 11 andwhich can also be used as dead sheathing, are provided with guidingstrips 35 (FIG. 7) which overlap when the wall segments are assembled.

On the side facing the inner chamber, the inner lining 21 and the uppersurface of the lower insert 12 are covered with a shell 26 made ofaustenitic steel, for example. At the upper end of the vessel, the steelshell 26 protrudes upwardly between the lining 21 and the upper insert13 and is secured to the lining 21 by means of a suitable, preferablybeaded, Weld 27 (FIG. 3). The upper end block 13, which is made of steelfor example, and the outer surface of which conforms with theellipsoidal shape of the vessel, is provided with an access opening 22,as shown in FIG. 3. In order to prevent the upper end block from fallinginto the vessel, While the vessel is not pressurized, there is provided,for example, an annular supporting member 23 to which the end block issecured for example with screws. The lower end block 12 which is made ofconcrete, for example, or both the lower and upper end blocks are formedwith feed-through passages 24 for the inlet and discharge pipes whichcarry the coolant needed in the operation of the reactor 4and for therequired electrical wiring (FIG. 3).

Complete tensioning of the annular cable 18 to the full prestressingcondition with the help of the bracing turnbuckles for example, is notfeasible because of the wide angle of encirclement by the cable.Therefore, in order to effect the necessary prestressing I propose adifferent procedure which is in accordance with my invention. With mymethod the annular cables are at first only stressed to such an extentthat they will be pulled fairly tight. Then the inner chamber, which iscoated with the sheathing of steel plate 26, or a rubber ballooninserted in the inner chamber, is filled with water and brought upgradually to the full rated pressure, preferably with due allowance forfrictional effects and the like. The casing segments 11 are therebyradially outwardly displaced from one another and the annular cables areresiliently stretched until full counter-tension Or prestressing isachieved. The gaps 25 (FIG. 8) which consequently form between the wallsegments and the joints 23 which face the concrete and which are widenedso that a gap is formed between the metal plates, are pressure-filledwith concrete (FIG. 9), so that even after the inner pressure isrelieved prestressing of the annular cables is maintained. With theapplication of the pressure, the conical end blocks 12, 13 are displacedfrom each other in the axial direction of the vessel. The curvature ofthe conical wall surface or outer surfaces of the end blocks musttherefore be pre-selected to suit this final assembly condition. The endblocks are mainly stressed in compression and only slightly subjected tobending. To elect uniform prestressing of the annular cables, therelative elongation (AL/L) of all the annular cables must be equal.Since the diameters of the individual annular cables are different, theabsolute elongation when the wall segments are radially outwardlydisplaced is the same for all of the annular cables, but the respectiverelative elongations thereof are consequently quite different. In orderthat the relative elongation of the various annular cables should be thesame, all of the annular cables are, for example, initially stressed tothe same amount of tension by suitably tightening the prestressing lockmeans or turnbuckles, and then the stress of the cables of smallerdiameter is reduced by turning the turnbuckles a predetermined number ofturns.

The embodiment of FIGS. 3 and 4 corresponds for the most part with theembodiment of FIGS. 1 and 2, except that the outer surfaces of the wallsegments 11 are formed in such a manner that the outer peripheralsurface of the vessel is of a cylindrical configuration which tapersslightly in the upward direction. Only half of the ring 23 supportingthe upper end block 13 is shown in FIG. 3 so that the weld 27 can beseen. Due to the cylindrical form of the outer vessel Wall in theembodiment of FIGS. 3 and 4, the above-mentioned difficulties regardinguniform prestressing of the annular cables 18 are not applicable forthis embodiment. The cables 18 which are out in suitable lengths andsecured with their ends by splicing or any other fastening means to formrings or loops, are pushed from above down around the outer wall surfaceof the vessel. The desired prestressing is then achieved in the mannerdescribed above with regard to the embodiment of FIG. 1.

A particularly desirable feature is that the outer surface of the vesselcan be formed into steps while nevertheless retaining the basicellipsoidal outline, and the prestressing means of the second kind, forexample annular cables, can be supported on the cylindrical steppedsurfaces. The ends of the wall segments then project over the outer endsurface of the inserts.

The pressure vessel shown in FIG. 5 differs from the vessel of FIG. 1 inthat its outer wall surface, while retaining its general ellipsoidaloutline, is formed with steps. In this way, the masses of concrete thatare found at the ends of the casing segments 11 in the embodiment ofFIG. 3 are avoided. The bracing wires 15 which are provided within thewall segments are located on the outside of the neutral chamfer line.Under the prestressing action, the wall segments 11 are bent outwardlyas is shown in FIG. 6 by the dot-and-dash lines 30. The deiiection atthe ends of the wall segments is approximately 1 to 2 cm. for a lengthof about 14 m. The steps that are located on the outside of the wallsegments 11 and which start at the center of the vessel and extend bothupwardly and downwardly thereon, form cylindrical surfaces 31 whichtaper slightly in a direction toward the ends of the wall segments. Theannular cables 29 for the upper half of the vessel can be fitted thereonfrom above after assembly of the vessel, while the annular cables 29 forthe lower half of the vessel, which are prepared in advance on the base32 thereof before the vessel is assembled, are fitted on the respectivecylindrical surfaces from below after the vessel is assembled. All ofthe annular cables 29 are of such predetermined lengths that they areseated on the respective cylindrical surfaces with substantially thesame tight fit. When liuid is pumped into the vessel in order tosuitably prestress the annular cables, the relative elongation of theupper and lower cables, which are of a smaller diameter, is somewhatgreater than the relative elongation of the annular cables which arelocated adjacent the middle portion of the vessel. Consequently, abending moment is exerted on the casing segments 11 which counteractsthe defiection caused by the longitudinally extending wires 15. Whencorrectly measured, both bending moments are equal. By backwardlybending the ends of the wall segments, the relative elongation of allthe annular cables can be made the same in the final condition so thatall the annular cables are equally stressed. In the region of the upperand lower end blocks 12, 13, the pressure exerted on the inner surfacesof the wall segments is greater than in the center portion thereof. Inorder to be able to place at these ends as great a number of annularcables or cable loops as possible, these ends are made to project abovethe outer faces of the end blocks 12, 13.

In FIG. 6 there is shown a single Wall segment 11 in non-stressedcondition (as indicated by the solid line 33), as prestressed bylongitudinally extending cables (the dot-and-dash line 30), and slightlydisplaced, as stressed by longitudinally extending cables and annularcables (the broken line 34).

In FIGS. 7 to 9 are shown the stages, on an enlarged scale and insection, that the inner lining 21 of the pressure vessel goes through inthe course of its production. FIG. 7 shows the inner surface of the Wallsegments clad with a steel plate 21, the abutting edges of which areoffset, so that the respective extensions 35 of the steel plates overlapeach other after the wall segments 11 have been assembled. On the insideof the vessel, the steel plates are covered with a thin layer 26consisting of austenitic steel, for example. The extensions 35 are soformed that they remain in overlapping engagement with one another evenafter the fluid has been pumped into the pressure vessel until the ratedpressure is reached, as shown in FIG. 8. Gaps 25 are formed between thewall segments 11 and gaps 28 and 36 are formed between the steel plates21 as fluid is pumped into the pressure vessel. Adjacent the gaps 36',slight grooves or indentations 37 form in the thin layer 26. The gaps 25and 28 are filled with concrete as shown in IFIG. 9, the fillingoperation taking place as long as the pressure vessel remains underpressure. After the pressure is relieved, the thin layer 26 is milled orcut along the grooves 37 and then subsequently removed. The thus freelyexposed gaps 36 are filled, as shown in FIG. 9 with filler strips 38consisting of steel, which are preselected to exactly tit the dimensionsof the gaps 36. After the steel strips 38 have been inserted, the innersurface of the steel plates is covered with a new layer 39l ofaustenitic steel which constitutes the final inner cladding or sheathingof the pressure vessel.

FIGS. and 11 also illustrate sections of the inner lining of a pressurevessel constructed in accordance with my invention. The sections show acooling pipe 40, arranged for example in meandering form on the side ofthe steel plate 21 which faces the wall segment. The coolant which flowsthrough the cooling pipe can be either liquid or gaseous.

If instead of one thick steel .plate 21, several thin plates such as thetwo plates 41, 42 (FIG. l2) are used, then for example cooling channels43 can be provided on the side of one of the plates which faces theother plate. FIG. 13 shows a further embodiment of my invention in whichthe inner lining of the vessel is formed of several layers,

for example of live layers (not including the layer 39 which is ofaustenitic steel) The three inner layers of the lining are made up ofsubstantially identical plates 44, for example. The lateral edges ofboth outer layers 45, 46 are welded to offset strips or ledges 47 whichform the abutting edges for the respective adjoining parts associatedwith each wall segment 11. The plates 44 in each of the inner layers arelmaintained in spaced relationship with respect to each other -by thebolts 48. Gaps 49 which are thus formed between the individual platesand are located in staggered relationship with respect to each other,and which are also formed between some of the plates and the ledges 47may be used as cooling channels.

When constructing the ellipsoidal pressure vessel, the wall segments andthe upper and lower inserts are assembled on a previously prepared baseat. the construction site of the reactor, and annular cables are thenapplied thereto. Afterwards, the inner chamber of the pressure vessel isclad with a closely fitting shell, for example consisting of steelsheets and is gradually filled with water until the rated pressure isreached, preferably with due allowance being given to friction effectsand the like. Instead of a sheet #metal shell, a rubber balloon can beemployed. During the pumping, the wall segments are radially expandedand pushed apart from one another so that the annular cables areelastically stretched until the full counter-tension is reached.Assuming an inner diameter of approximately 7 m., the radial expansionis about 15 mm. and the gap between the individual wall segments isabout 6 mm. These gaps are `filled with concrete so that after thepressure is relieved, the prestressing effect of the annular cables ismaintained. The gaps which arise bet-ween the adjacent end faces of thesteel plates by pumping fiuid into the vessel and by the consequentsliding of the guiding ledges of the steel plates on one another duringthe prestressing operation, are filled with filler strips consisting ofsteel. The gaps between the adjacent edges of the steel plates arenoticeable from Iwithin by slight indentations of the sheet metal shell.The metal shell is milled or cut along these indentations in order topermit insertion of the filler strips therein. After the gaps have beenthus filled this metal shell is replaced with a final austenitic steelshell. For guiding the wall segments on the base plate, central guiderails are provided on the individual wall segments so that the wallsegments can slide thereon in the radial direction while the inflationis taking place.

The various components of the pressure vessel embodying my invention canbe prefabricated. Consequently, the size of the casing segments can bepreselected so as to be suitable for available transportationfacilities. No cable prestressing or tensioning equipment is necessaryat the installation site of the pressure vessel since the bracing wiresthat are embedded in the wall segments have been previously prestressedand since the annular cables or all of the prestressing members areprestressed by pumping uid into the pressure vessel, after the vesselhas been assembled. In prestressing the annular cable, the frictionlosses which otherwise amount to as -much as 20% are practically equalto zero. Since the prestressing elements are either embedded deep in theouter concrete layers of the wall segments or are located on the outersurface of the pressure vessel respectively, high-grade steels can beused for the prestressing elements without hesitation. The prestressingelements which lie on the outside are furthermore readily accessible forinspection, and by lowering the upper insert, a fairly large accessopening is made available for assembly and mounting purposes andpossibly also for reactor maintenance and repair work that may berequired at a later time. The prefabricated components and theconsequent facilitation of the assembly process result in considerablereduction in the time needed for constructing a vessel of this type.Furthermore, the aggregate costs of a pressure vessel of this type isroughly not even half as much as the cost of constructing acorresponding steel vessel.

While =my invention has been illustrated and described as a method ofmanufacturing a pressure vessel of prestressed concrete for nuclearreactors, it is not intended to lbe limited to the details shown, sincevarious modifications in my method `may be made without departing in anyway from the spirit of the present invention. Such adaptations shouldand are intended to be comprehended within the meaning and range ofequivalents of the following claims.

I claim:

1. A method of manufacturing a prestressed concrete pressure vessel fornuclear reactors, which comprises assembling the pressure vessel in situfrom prefabricated components including prestressing elements andconcrete wall segments having adjacent edge portions the prefabricatedcomponents being so formed as to provide an opening at respective upperand lower ends of said vessel, introducing an elastic inflatablecontainer into the interior of said pressure vessel; covering theadjacent edge portions of said wall segments with strips ofpressure-resistant material; inflating said container by pumping fluidtherein so as to expand said vessel and form gaps between the edgeportions of said wall segments, and filling said gaps with apressure-resistant material, the method also comprising the steps oflining the interior surface of said vessel with a layer of steel plateshaving adjacent edges and, after prestressing the vessel, lining saidlayer of steel plates with a layer of austenitic steel projecting out ofsaid upper opening, and sealingly connecting said layer of steel platesand said layer of austenitic steel outside of said upper opening.

2. Method according to claim 1 wherein the interior surface of saidVessel is lined with a plurality of steel plates having edges providedwith guiding strips and place ing said steel plates -with said edgesadjacent one another so that the respective guiding strips overlap.

3. Method according to claim 1 including closing the lower opening witha tightly inserted closure member and closing the upper opening with aremovable cover memlber.

4. Method according to claim 3 wherein the prefabricated Iwall segmentsare so formed that the outer surface of the assembled vessel isellipsoidal and is formed with substantially cylindrical stepped tiers,and the vessel wall projects beyond the outer surface of said closureand cover members, and which includes prestressing the vessel with agroup of annular prestressing elements located on the stepped tiers.

References Cited UNITED STATES PATENTS 1,964,870 7/1934 Chappell 264-322,597,084 5/1952 Huddleston 264-32 1,189,694 7/1916 Janssen et al.52-224 2,959,895 1l/1960 Caubet 52-224 2,683,914 7/1954 Reimbert 264-228X 2,755,630 7/1956 Freyssinet 264-228 X 2,771,655 11/1956 Nervi 264-2282,903,877 9/1959 Meade 264-228 X 3,260,020 7/1966 Patin 52-224 X FOREIGNPATENTS 800,388 8/1958 Great Britain.

ROBERT F. WHITE, Primary Examiner.

FRANK L. ABBOTT, Examiner.

A. C. PERHAM, I. A. FINLAYSON, J. H. SILBAUGH,

Assistant Examiners.

1. A METHOD OF MANUFACTURIN A PRESTRESSED CONCRETE PRESSURE VESSEL FORNUCLEAR REACTORS, WHICH COMPRISES ASSEMBLING THE PRESSURE VESSEL IN SITUFROM PREFABRICATED COMPONENTS INCLUDING PRESTRESSING ELEMENTS ANDCONCRETE WALL SEGMENTS HAVING ADJACENT EDGE PORTIONS THE PREFABRICATEDCOMDPONENTS BEING SO FORMED AS TO PROVIDE AN OPENING AT RESPECTIVE UPPERAND LOWER ENDS OF SAID VESSEL, INTRODUCING AN ELASTIC INFLATABLECONTAINER INTO THE INTERIOR OF SAID PRESSURE VESSEL; COVERING THEADJACENT EDGE PORTIONS OF SAID WALL SEGMENTS AND STRIPS OFPRESSURE-RESISTANT MATERIAL; INFLATING SAID CONTAINER BY PUMPING FLUIDTHEREIN SO AS TO EXPAND SAID VESSEL AND FORM GAPS BETWEEN THE EDGEPORTIONS OF SAID WALL SEGMENTS, AND FILLING SAID GAPS WITH APRESSURE-RESISTANT MATERIAL, THE METHOD ALSO COMPRISING THE STEPS OFLINING THE INTERIOR SURFACE OF SAID VESSEL WITH A LAYER OF STEEL PLATESHAVING ADJACENT EDGES AND, AFTER PRESTRESSING THE VESSEL, LINING SAIDLAYER OF STEEL PLATES WITH A LAYER OF AUSTENITIC STEEL PROJECTING OUT OFSAID UPPER OPENING, AND SEALINGLY CONNECTING SAID LAYER OF STEEL PLATESAND SAID LAYER OF AUSTENITIC STEEL OUTSIDE OF SAID UPPER OPENING.